Yellowfin tuna has a soft dorsal and anal fins and bright yellow finlets. They are usually found in open water tropical and subtropical sea and can go as deep as 100 fathoms. The best time to fish yellowfin tuna is during summer for there number oscillates in the annual catch. They can grow up to 440 lbs and as long as 94 in. Trolling is the best fishing method to catch a yellowfin tuna.